Method for purifying 1,5-pentanediamine and 1,5-pentanediamine

ABSTRACT

Provided is a method for purifying 1,5-pentanediamine comprising: providing 1,5-pentanediamine to be purified and treating the 1,5-pentanediamine to be purified by a reduction reaction to obtain purified 1,5-pentanediamine. Meanwhile, further provided is 1,5-pentanediamine prepared by the method. The purification method has a concise process and a simple operation, and is suitable for industrial production, and can significantly improve the quality of 1,5-pentanediamine.

TECHNICAL FIELD

The present invention relates to a method for purifying1,5-pentanediamine, and 1,5-pentanediamine obtained by the method.

BACKGROUND

Pentanediamine (pentanediamine mentioned in the present invention refersto 1,5-pentanediamine, alias 1,5-diaminopentane, pentamethylene diamine,cadaverine) is an important chemical intermediate, mainly used as amonomer for preparing polymers such as polyamides, an organic synthesisintermediate, and an epoxy resin curing agent, and also used forbiological research. Nylons, which are obtained by polymerization of1,5-pentanediamine, can be used in many aspects of daily production andlife, such as electronic appliances, mechanical equipment, andautomobile parts.

Industrially, the process for preparing 1,5-pentanediamine is asfollows: a solution of 1,5-pentanediamine salt is obtained byfermentation or enzymatic conversion process; the salt solution istreated by adding alkali, extraction and evaporation and the like toobtain an aqueous solution of 1,5-pentanediamine, followed bydistillation to give 1,5-pentanediamine. In the preparation of1,5-pentanediamine, in addition to 1,5-pentanediamine, by-productscontaining an unsaturated bond, such as 2,3,4,5-tetrahydropyridine(THP), are also produced.

In the process for preparing nylons with 1,5-pentanediamine as thestarting material, the presence of the unsaturated by-product THP wouldaffect the subsequent polymerization of 1,5-pentanediamine, therebyreducing the product quality of the polymer such as nylon 56. Inparticular, THP would cause the discoloration or branching of thepolymer. Thus, reducing the amount of impurity THP in the1,5-pentanediamine product can avoid the discoloration of the polymerand is critical to the improvement of the quality of the polymerproduct.

In the prior art relating to the removal and effective control ofimpurity THP, as described in EP 26684867 of Mitsui Chemicals, the fattyalcohols having 4 to 7 of carbon atoms are used as extractant to extract1,5-pentanediamine from a fermentation broth, which can effectivelyreduce the THP content in the 1,5-pentanediamine products. Takingn-butanol as an example, the extraction rate thereof is 91.6%, thecontent of THP in the product is 0.1 wt %; and when using isobutanol assolvent, the extraction rate is 86.0%, the content of the impurity THPin the product is 0.1 wt %, and when using chloroform as extractant, theextraction rate is only 61.7%, the content of the impurity THP in theproduct is 0.6 wt %. Although the extraction by fatty alcohol with 4 to7 of carbon atoms may obtain a better result than using chloroform asextractant, such extraction still has some defects such as relativelylow extraction rate, difficulty in the separation of the layers, andhigh energy consumption in recovery of the extractant, and is notsuitable for large-scale production.

As described in CN102449029 of TORAY INDUSTRIES, INC., the polyamideresins obtained by polymerizing 1,5-pentanediamine having a totalcontent of 0.1% of THP and piperidine have better performance andquality, wherein the extraction process of the amine raw material iscarried out by using chloroform as extractant and further distillationunder reduced pressure to obtain 1,5-pentanediamine with the totalcontent of impurities THP and piperidine less than 0.1%. Clearly, theextraction rate of chloroform is relatively low, as a result, a largeamount of 1,5-pentanediamine present in the aqueous phase is noteffectively extracted, thus the product yield is low, and the loss issignificant.

Therefore, how to remove and effectively control the content of impurityTHP in 1,5-pentanediamine products has become a key factor incontrolling the quality of 1,5-pentanediamine products and a “bottleneck” for improving the quality of nylon products prepared by1,5-pentanediamine.

SUMMARY OF THE INVENTION

In order to solve the technical problems mentioned above, the presentinvention provides a method for purifying 1,5-pentanediamine,comprising: providing 1,5-pentanediamine to be purified; and treatingsaid 1,5-pentanediamine to be purified by use of reduction reaction, toobtain a purified 1,5-pentanediamine.

According to an embodiment of the present invention, the1,5-pentanediamine to be purified contains 2,3,4,5-tetrahydropyridineimpurity.

According to another embodiment of the present invention, the content of2,3,4,5-tetrahydropyridine impurity in the purified 1,5-pentanediamineis less than 0.05 wt %.

According to another embodiment of the present invention, the content ofthe 2,3,4,5-tetrahydropyridine impurity in the purified1,5-pentanediamine is less than 0.03 wt %.

According to another embodiment of the present invention, the purified1,5-pentanediamine contains piperidine.

According to another embodiment of the present invention, thepurification further comprises a distillation step to remove piperidineformed by the reduction of 2,3,4,5-tetrahydropyridine, so as to keep thecontent of piperidine in the purified 1,5-pentanediamine less than 0.05wt %, based on the weight of 1,5-pentanediamine in the1,5-pentanediamine to be purified.

According to another embodiment of the present invention, the content ofpiperidine in the purified 1,5-pentanediamine is less than 0.03 wt %.

According to another embodiment of the present invention, the reductionreaction is an electrochemical reduction or a reduction with reducingagent, and the reducing agent is hydrogen gas or metal hydride.

According to another embodiment of the present invention, the metalhydride is one or more selected from the group consisting of NaBH₄,KBH₄, and LiAlH₄.

According to another embodiment of the present invention, when the metalhydride is used as the reducing agent, the reaction temperature is from0 to 25° C., the reaction time is from 0.5 to 1 hour, and the metalhydride is from 1 to 2 times of 2,3,4,5-tetrahydropyridine in the1,5-pentanediamine to be purified in the amount of substance.

According to another embodiment of the present invention, when hydrogengas is used as the reducing agent, a nickel-based catalyst or aplatinum-based catalyst is used simultaneously.

According to another embodiment of the present invention, the reductionreaction is carried out by a fixed bed hydrogenation or a fluidized bedhydrogenation.

According to another embodiment of the present invention, when a fixedbed catalytic hydrogenation is used, the pressure of the hydrogen isfrom 0.5 to 12 MPa and the reaction temperature is from 40 to 110° C.

According to another embodiment of the present invention, when afluidized bed catalytic hydrogenation is used, the pressure of thehydrogen gas is from 0.5 to 15 MPa and the reaction temperature is from40 to 110° C.

In another aspect, the present invention provides 1,5-pentanediamineprepared by the method according to any one of the embodiments mentionedabove.

The present method for purifying 1,5-pentanediamine is of conciseprocess and simple operation, is suitable for industrial production, andcan improve the quality of 1,5-pentanediamine product remarkably.

DETAILED DESCRIPTION OF THE INVENTION

Typical examples illustrating the features and advantages of the presentinvention will be described in detail in the following description. Itshould be understood that the invention can have various changes invarious embodiments without departing from the scope of the inventionand the description herein is by way of illustration only and is notintended to limit the invention.

The fermentation broth or enzyme conversion solution containing1,5-pentanediamine is subjected to extraction and distillation to obtainthe 1,5-pentanediamine to be purified, which contains2,3,4,5-tetrahydropyridine impurity. In order to eliminate the effect ofthe impurity on the subsequent polymerization producing nylon, in thepresent invention, the 1,5-pentanediamine to be purified containingabove-mentioned impurity is subject to reduction treatment to convert2,3,4,5-tetrahydropyridine therein to piperidine. By doing so, thecontent of 2,3,4,5-tetrahydropyridine impurity in the purified1,5-pentanediamine is less than 0.05 wt %, or even less than 0.03 wt %,and 1,5-pentanediamine product with a high quality is obtained, whichmeets the stringent requirements for 1,5-pentanediamine monomer in thepreparation of polymers such as nylon.

The present invention provides a method for purifying 1,5-pentanediaminecomprising: providing 1,5-pentanediamine to be purified; and treatingsaid 1,5-pentanediamine to be purified by use of reduction reaction toobtain purified 1,5-pentanediamine.

In the present invention, the 1,5-pentanediamine to be purified contains2,3,4,5-tetrahydropyridine impurity.

In the present invention, after the reduction of 1,5-pentanediamine tobe purified, 2,3,4,5-tetrahydropyridine is reduced to piperidine. Theboiling point of piperidine is significantly different from that of1,5-pentanediamine, which makes them to be easily separated in thesubsequent distillation process, such that the content of piperidine inthe purified 1,5-pentanediamine is controlled at a level of no more than0.05 wt % relative to 1,5-pentanediamine, preferably no more than 0.03wt %, the content is in weight percentage and is based on the weightpercentage of 1,5-pentanediamine in the purified 1,5-pentanediamine. Dueto the absence of unsaturated bond in piperidine, there is nosignificant effect on the subsequent polymerization of pentanediamineduring the actual production, and thus the conversion of2,3,4,5-tetrahydropyridine to piperidine is also of significance inpractical production.

In the present invention, the 1,5-pentanediamine to be purified, whichcontains 2,3,4,5-tetrahydropyridine as impurity, may present in form of1,5-pentanediamine containing 2,3,4,5-tetrahydropyridine impurity, or anorganic solution or an aqueous solution thereof. In particular, the1,5-pentanediamine to be purified can be obtained by basifying asolution containing 1,5-pentanediamine salt, followed by extraction orevaporation, and the content of 1,5-pentanediamine, except the solventand water, is more than 99%.

In the present invention, there is not particular limit to the source ofthe 1,5-pentanediamine to be purified. The 1,5-pentanediamine to bepurified can be prepared by chemical methods. Suyama et al. (The methodof decarboxylation of lysine, fourth edition, Yakugaku Zasshi (1965),Vol. 85(6), pp, 531-533) discloses a process in which the lysine isboiled in cyclohexane containing tetrahydronaphthalene peroxides toproduce pentanediamine. Japanese Unexamined Patent Publication (Kokai)No. SHO-60-23328 discloses a method for producing pentanediamine fromlysine using vinyl ketone compounds of 2-cyclic vinyl ester as acatalyst. Pentanediamine can also be prepared by biological methods. Forexample, an enzymatic conversion solution is obtained by the action ofpentanediamine decarboxylase on lysine, and thereby extractingpentanediamine (See JP 200400114A). The resulting lysine can besimultaneously converted to pentanediamine during the fermentation byup-regulating the expression of lysine decarboxylase in alysine-producing strain, for example by gene technology, or byrecombinant expression of lysine decarboxylase, and thus pentanediaminefermentation broth is obtained by direct fermentation (See Constructionof Recombinant Corynebacterium glutamicum Producing 1,5-Pentanediamineby One Step Method, Niu Tao, et al., CHINA BIOTECHNOLOGY, 2010, 30 (8):93-99).

In the present invention, there is not particular limit to the methodfor producing the 1,5-pentanediamine to be purified, and anyconventional method can be used. A solvent method, for example, can beused, which comprises the following steps: adding a base to the solutionof the pentanediamine salt to adjust the pH value thereof; using asolvent to extract the pentanediamine therefrom; and separating thepentanediamine from the solvent (see JP 200400114A, JP2004222569A,CN101981202A). A precipitation method, for example, can be used, whichcomprises the following steps: mixing a solution of pentanediamine witha base to form pentanediamine phase and aqueous phase, and separatingthe pentanediamine from the pentanediamine phase (See JP2009096796A,JP2009131239A). A membrane filtration method, for example, can be used,which comprises the following steps: adding a base into a solution ofthe pentanediamine salt to adjust the pH value thereof; using anano-membrane to filtrate the salt out; and obtain the aqueous solutionof pentylenediamine accordingly (see CN101970393A). Also, a reactionprocess, for example, can be used, which comprises the following steps:subjecting the pentanediamine into a reaction to give a more readilyseparated compound; separating the compound therefrom; and reducing theresulting compound into pentanediamine (see CN102712569A, CN102056889A).In addition, CN101356151A discloses the addition of sufficient amount ofammonia or hydrazine into the pentanediamine salt to form a liquid phaseof pentanediamine and ammonia/hydrazine and a solid phase of aninorganic salt, followed by separation and extraction of pentanediamine.

In the present invention, the method for extracting or preparing thepentanediamine to be purified is not particularly limited. For example,the method disclosed in PCT/CN2013/071044, PCT/CN2013/071045,JP2009096796A, JP 2009131239 A and the like, can be used.

The organic solvent used to dissolve and extract 1,5-pentanediamine inthe present invention refers to the one which does not react with1,5-pentanediamine, maintains inert during the chemical hydrogenationreduction and has a certain solubility to 1,5-pentanediamine.Conventional chemical solvents may be alcoholic solvent such as ethanoland butanol.

In the present invention, there is no limit the way for carrying out thereduction reaction. A reduction reaction can be carried out by using achemical reducing agent or by electrochemical reduction. The reducingagents include, but not limited to, active metal elements such as Na,Al, Zn, Fe and the like, metal hydrides such as lithium aluminum hydride(LiA1H₄), sodium borohydride (NaBH₄), zinc borohydride (Zn(BH₄)₂),potassium borohydride (KBH₄) and the like, reductive non-metallicsubstances such as H₂, C, Si, etc., alkali metal elements such as Li,Na, K and the like, reductive oxides such as CO, SO₂, H₂O₂ and the like,non-metallic hydrides such as H₂S, NH₃, HCl, CH₄, and the like,reductive salts such as Na₂SO₃, FeSO₄ and the like, and other reductivesubstances such as stannous chloride (SnC1₂), oxalic acid (H₂C₂O₄),ethanol (C₂H₅OH) and the like.

In one embodiment of the present invention, the reducing agent ishydrogen gas. In particular, the 1,5-pentanediamine to be purified andhydrogen gas can be passed through a fixed bed packed with a catalyst;1,5-pentanediamine to be purified and hydrogen gas can also be reactedin a fluidized bed reactor having the catalyst. In another embodiment ofthe present invention, the reducing agent is a metal hydride, and the1,5-pentanediamine to be purified and the metal hydride are mixed andheated to remove 2,3,4,5-tetrahydropyridine, wherein the metal hydrideincludes, but is not limited to, NaBH₄, KBH₄, LiA1H₄, the amount ofsubstance of which is about from 1 to 2 times of that of2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to be purified.

In the present invention, the reduction reaction conditions of the metalhydride are as follows: the amount of the metal hydride to be addeddepends on the content of 2,3,4,5-tetrahydropyridine in1,5-pentanediamine, and is about from 1 to 2 times of2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to be purified inthe amount of substance. The reaction temperature is between about 0° C.and 90° C., preferably about 20° C. and 60° C. If the temperature is toohigh, although the reaction is accelerated, some side-reactions may takeplace, which would increase the impurities in the pentanediamine. Thereaction time is about from 0.5 to 1 hour.

In the present invention, a protic solvent such as water, alcohol andthe like may be added in an amount of 1% to 15% by weight of the metalhydride as a co-solvent for the metal reducing agent.

In the present invention, after the reduction reaction, distillation canbe continued to further remove the reaction product and purify1,5-pentanediamine. The distillation step can be a combination of one ormore operations in vacuum distillation, flashing, and distillation.

In the present invention, when the reducing agent is hydrogen gas, afixed bed hydrogenation or a fluidized bed hydrogenation may be used.The catalyst may be a nickel-based catalyst, a platinum-based catalyst,or other catalyst suitable for catalytic hydrogenation. The catalyst ofthe present invention is preferably a nickel-based catalyst, and morepreferably a supported nickel-based catalyst, wherein the carrier may bealuminum or alumina, or it may be a natural mineral such as diatomaceousearth, or an adsorbent such as activated carbon.

In the invention, the preferred process conditions for the purificationby using the fixed bed catalytic hydrogenation are: hydrogen pressure of0.5 to 10 MPa, and the reaction temperature of hydrogenationpurification of 40 to 110° C.

In the present invention, the preferred process conditions for thepurification by using the fluidized bed catalytic hydrogenation are:hydrogen pressure of 0.5 to 15 MPa, the reaction temperature ofhydrogenation purification of 40 to 110° C., the addition amount of thecatalyst of 0.1 wt % to 5 wt % based on the weight of 1,5-pentanediaminein the 1,5-pentanediamine to be purified.

In the invention, 2,3,4,5-tetrahydropyridine impurity is converted intosaturated piperidine by chemical reduction. The content of2,3,4,5-tetrahydropyridine in 1,5-pentanediamine is reduced to less than0.1% by weight, preferably less than 0.05% by weight, more preferablyless than 0.03% by weight, or even less than 0.01% by weight. The damageof 2,3,4,5-tetrahydropyridine to polymerization producing nylon iseliminated. The piperidine produced by reduction reaction can beseparated from 1,5-pentanediamine in subsequent distillation. The impactof piperidine without unsaturated bond on polymerization producing nylonis much lower than that of 2,3,4,5-tetrahydropyridine. There is nearlyno 1,5-pentanediamine product lost, and not any more purity except2,3,4,5-tetrahydropyridine would be produced in the process. The presentinvention can effectively remove impurities at a lower cost to obtain apurified 1,5-pentanediamine product with high quality.

After converting 2,3,4,5-tetrahydropyridine impurity into piperidine bythe reduction method in the present invention, the resulting purifiedpentanediamine can further remove the converted piperidine, or isdirectly subjected to a subsequent process without removing piperidine.The method for removing piperidine includes, but is not limited to, useof ion exchange resins, activated carbon adsorption, extraction, ordistillation extraction, etc. The above-mentioned method for removingpiperidine may be used alone or in combination of two or more.

The metal reducing agent of the invention can directly supply a hydrogensource, and an imine can be conveniently reduced to amine without anadditional catalyst. The reaction condition is mild, the process andoperation is simple and the method is suitable for large-scaleindustrial production.

The invention will now be described in detail by way of specificexamples to make the features and advantages of the invention clearer.But the invention is not limited to the examples given herein.

Among them, the 1,5-pentanediamine to be purified in the followingexamples can be obtained by extraction or distillation. Specifically,reference may be made to PCT/CN2013/071044, PCT/CN 2013/071045, JP2009096796 A, JP 2009131239 A and the like.

The method for preparing the fermentation broth used in the examples canbe found in Patent PCT/CN 2013/071044, PCT/CN2013/071045, JP 2009096796A, JP 2009131239 A and the like.

In the examples and comparative examples listed herein, the followingtest methods were used:

1. Pentanediamine Gas Chromatography (GC)

The test methods for pentanediamine and 2,3,4,5-tetrahydropyridine:

See CN102782146 A, using gas phase normalization method.

2. Nylon color detection method:

GB-T 2409-1980, using KONICA MINOLTA CM-3600A instrument.

Example 1

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine to be purified in a massconcentration of 99%. The 1,5-pentanediamine to be purified contained500 mg organic impurity 2,3,4,5-tetrahydropyridine (THP) (6 mmol, 0.2 wt%, based on the weight of 1,5-pentanediamine in the 1,5-pentanediamineto be purified). Then, 240 mg NaBH₄ (6 mmol) was added to the roundbottom flask. The temperature of the solution in the flask wascontrolled at 5 to 10° C. After stirring for 1 hour, a small amount ofwater was added to quench the reaction.

1,5-pentanediamine in the solution after chemical reduction reaction wassampled and analyzed. The analytical results showed that1,5-pentanediamine had a purity of 99.41%, the content of THP was 0.06wt % and the content of piperidine was 0.16 wt % (normalized).

The above-mentioned reduced 1,5-pentanediamine solution was subjected todistillation, and 1,5-pentanediamine was further separated frompiperidine impurity to obtain the purified 1,5-pentanediamine.

The purified 1,5-pentanediamine was detected by GC. The results showedthat 1,5-pentanediamine had a purity of 99.86 wt %, the content of THPwas 0.06 wt % and the content of piperidine was 0.05 wt % (normalized).

Example 2

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine to be purified in a massconcentration of 99%. The 1,5-pentanediamine to be purified contained500 mg organic impurity THP (6 mmol, 0.2%). 25 mL of methanol and 240 mgof NaBH₄ (6 mmol) were added to the round bottom flask, and thetemperature of the solution in the flask was controlled at 0 to 10° C.After stirring for 1 hour, a small amount of water was added to quenchthe reaction.

1,5-pentanediamine in the solution after chemical reduction reaction wassampled and analyzed. The analytical results showed that1,5-pentanediamine had a purity of 99.46%, the content of THP was 0.05%,the content of piperidine was 0.15% (normalized).

The above-mentioned reduced 1,5-pentanediamine solution was subjected todistillation, and 1,5-pentanediamine was further separated from thepiperidine impurity to obtain purified 1,5-pentanediamine.

The purified 1,5-pentanediamine was detected by GC. The results showedthat 1,5-pentanediamine had a purity of 99.89%, the content of THP was0.05% and the content of piperidine was 0.02% (normalized).

Example 3

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine to be purified in a massconcentration of 99%. The 1,5-pentanediamine to be purified contained500 mg organic impurity THP (6 mmol, 0.2%). 30 mL of purified water and240 mg of NaBH₄ (6 mmol) were added to the round bottom flask, and thereaction temperature was controlled at 10 to 15° C. After stirring for0.5 hour, a small amount of water was added to quench the reaction.

1,5-pentanediamine in the solution after chemical reduction reaction wassampled and analyzed. The results showed that 1,5-pentanediamine had apurity of 99.32%, the content of THP was 0.04% and the content ofpiperidine was 0.15% (normalized).

The above-mentioned reduced 1,5-pentanediamine solution was subjected todistillation, and 1,5-pentanediamine was further separated from thepiperidine impurity to obtain purified 1,5-pentanediamine.

The purified 1,5-pentanediamine was detected by GC. The results showedthat 1,5-pentanediamine had a purity of 99.91%, the content of THP was0.04% and the content of piperidine was 0.01% (normalized).

Example 4

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine to be purified in a massconcentration of 99%. The 1,5-pentanediamine to be purified contained500 mg organic impurity THP (6 mmol, 0.2%). 480 mg of NaBH₄ (12 mmol)was added to the round bottom flask. After stirring at 15 to 20° C. for0.5 hour, a small amount of water was added to quench the reaction.

1,5-pentanediamine in the solution after chemical reduction reaction wassampled and analyzed. The analytical results showed that1,5-pentanediamine had a purity of 99.36%, the content of THP was 0.05%and a content of piperidine was 0.14% (normalized).

The above-mentioned reduced 1,5-pentanediamine solution was subjected todistillation, and 1,5-pentanediamine was further separated from thepiperidine impurity to obtain purified 1,5-pentanediamine.

The purified 1,5-pentanediamine was detected by GC. The results showedthat 1,5-pentanediamine had a purity of 99.90%, the content of THP was0.05% and the content of piperidine was 0.01% (normalized).

Example 5

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine to be purified in a massconcentration of 99%. The 1,5-pentanediamine to be purified contained500 mg organic impurity THP (6 mmol, 0.2%). 228 mg of LiA1H₄ (6 mmol)was added to the round bottom flask and a reduction reaction wasconducted at 20 to 25° C. for 1 hour with stirring. A small amount ofwater was added to quench the reaction.

1,5-pentanediamine in the solution after chemical reduction reaction wassampled and analyzed. The results showed that 1,5-pentanediamine had apurity of 99.45%, the content of THP was 0.03%, the content ofpiperidine was 0.16% (normalized).

The above-mentioned reduced 1,5-pentanediamine solution was subjected todistillation, and 1,5-pentanediamine was further separated from theimpurity piperidine to obtain purified 1,5-pentanediamine.

The purified 1,5-pentanediamine was detected by GC. The results showedthat 1,5-pentanediamine had a purity of 99.87%, the content of THP was0.03% and the content of piperidine was 0.03% (normalized).

Example 6

A solution of pentanediamine in butanol (the content of pentanediaminewas 6 wt %) prepared according to the extraction process of the Chinesepatent application publication CN101981202A was passed through adistillation apparatus to fractionate out butanol, so as to obtain1,5-pentanediamine to be purified. The content of 1,5-pentanediamine was98% and the content of THP was 0.21%.

A 100 mL nickel-based supported catalyst (CRI International Ltd.,KL6565) was charged in the middle of a stainless steel reactor having aninner diameter of 20 mm and a length of 720 mm. Quartz sands with aparticle size of 20 to 40 mesh were added as a support layer in thelower part of the reactor, and a small amount of 20 to 40 mesh quartzsands were added in the upper part of the reactor to adjust the liquiddistribution. The temperature was automatically controlled by usingelectric heating. After the catalyst was activated, the1,5-pentanediamine to be purified was mixed with hydrogen gas and passedthrough the catalyst bed from top to bottom. A catalytic hydrogenationreaction was carried out under the following conditions: the pressure ofhydrogen gas in reactor was controlled at 3 MPa (gauge pressure); thereaction temperature was kept in a range of from 50 to 80° C.; and thefeed flow rate of 1,5-pentanediamine to be purified was of 200 mL/hour.Thus, 2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to bepurified was converted to piperidine.

After reacting in above reactor, the reaction product flowing out fromthe outlet of the reactor was cooled, liquefied, and quantified by gaschromatography.

1,5-pentanediamine in the solution after catalytic hydrogenationreaction was sampled and analyzed. The results showed that1,5-pentanediamine had a purity of 99.51%, the content of2,3,4,5-tetrahydropyridine was 0.006%, and the content of piperidine was0.23% (normalized).

Example 7

A solution of pentanediamine in butanol (the content of pentanediaminewas 6 wt %) prepared according to the extraction process of the Chinesepatent application publication CN101981202A was passed through adistillation apparatus to fractionate out butanol, so as to obtain1,5-pentanediamine to be purified. The content of 1,5-pentanediamine was98% and the content of THP was 0.21%.

A 100 mL nickel-based supported catalyst (CRI International Ltd.,KL7767) was charged in the middle of a stainless steel reactor having aninner diameter of 20 mm and a length of 720 mm. Quartz sands with aparticle size of 20 to 40 mesh were added as a support layer in thelower part of the reactor, and a small amount of 20 to 40 mesh quartzsands were added in the upper part of the reactor to adjust the liquiddistribution. The temperature was automatically controlled by usingelectric heating. After the catalyst was activated, the1,5-pentanediamine to be purified was mixed with hydrogen gas and passedthrough the catalyst bed from top to bottom. A catalytic hydrogenationreaction was carried out under the following conditions: the pressure ofhydrogen gas in reactor was controlled at 0.5 MPa (gauge pressure); thereaction temperature was kept in a range of 100 to 110° C.; and the feedflow rate of 1,5-pentanediamine to be purified was of 50 mL/hour. Thus,2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to be purified wasconverted to piperidine.

After reacting in above reactor, the reaction product flowing out fromthe outlet of the reactor was cooled, liquefied, and quantified by gaschromatography.

1,5-pentanediamine in the solution after catalytic hydrogenationreaction was sampled and analyzed. The results showed that1,5-pentanediamine had a purity of 99.52%, the content of2,3,4,5-tetrahydropyridine was 0.003%, and the content of piperidine was0.20% (normalized).

Example 8

A solution of pentanediamine in butanol (the content of pentanediaminewas 6 wt %) prepared according to the extraction process of the Chinesepatent application publication CN101981202A was passed through adistillation apparatus to fractionate out butanol, so as to obtain1,5-pentanediamine to be purified. The content of 1,5-pentanediamine was98% and the content of THP was 0.21%.

A 100 mL nickel-based supported catalyst (CRI International Ltd.,KL7767) was charged in the middle of a stainless steel reactor having aninner diameter of 20 mm and a length of 720 mm. Quartz sands with aparticle size of 20 to 40 mesh were added as a support layer in thelower part of the reactor, and a small amount of 20 to 40 mesh quartzsands were added in the upper part of the reactor to adjust the liquiddistribution. The temperature was automatically controlled by usingelectric heating. After the catalyst was activated, the1,5-pentanediamine to be purified was mixed with hydrogen gas and passedthrough the catalyst bed from top to bottom. A catalytic hydrogenationreaction was carried out under the following conditions: the pressure ofhydrogen gas in reactor is controlled at 10 MPa (gauge pressure); thereaction temperature is kept in a range of 40 to 60° C.; and the feedflow rate of 1,5-pentanediamine to be purified is of 600 mL/hour. Thus,2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to be purified wasconverted to piperidine.

After reacting in above reactor, the reaction product flowing out fromthe outlet of the reactor was cooled, liquefied, and quantified by gaschromatography.

1,5-pentanediamine in the solution after catalytic hydrogenationreaction was sampled and analyzed. The results showed that1,5-pentanediamine had a purity of 99.47%, the content of2,3,4,5-tetrahydropyridine was 0.004%, and the content of piperidine was0.20% (normalized).

Example 9

A solution of pentanediamine in butanol (the content of pentanediaminewas 6 wt %) prepared according to the extraction process of the Chinesepatent application publication CN101981202A was passed through adistillation apparatus to fractionate out butanol, so as to obtain1,5-pentanediamine to be purified. The content of 1,5-pentanediamine was98% and the content of 2,3,4,5-tetrahydropyridine was 0.21%.

To a 5 L autoclave, 2 L of above-mentioned pentanediamine liquid wasadded, and then 1.6 g of activated skeleton nickel catalyst (made byJinzhou catalyst plant). The reaction was carried out for a total of 6hours under the hydrogen pressure in the autoclave being controlled at12 MPa (gauge pressure), with the reaction temperature of 105 to 110° C.and stirring. Then the catalyst was separated by precipitation to give asolution of the pentanediamine. The resulting product was quantified bygas chromatography.

1,5-pentanediamine in the solution after catalytic hydrogenationreaction was sampled and analyzed. The results showed that1,5-pentanediamine had a purity of 99.51%, the content of2,3,4,5-tetrahydropyridine was 0.01%, and the content of piperidine was0.18% (normalized).

Example 10

A solution of pentanediamine in butanol (the content of pentanediaminewas 6 wt %) prepared according to the extraction process of the Chinesepatent application publication CN101981202A was passed through adistillation apparatus to fractionate out butanol, so as to obtain1,5-pentanediamine to be purified. The content of 1,5-pentanediamine was98% and the content of THP was 0.21%.

To a 5 L autoclave, 2 L of above-mentioned pentanediamine liquid wasadded, and then 90 g of activated skeleton nickel catalyst (made byJinzhou catalyst plant) and 10 g of activated palladium-based supportedcatalyst (CRI International Ltd. KL7767) were added. The reaction wascarried out for a total of 2 hours under the hydrogen pressure in theautoclave being controlled at 12 MPa (gauge pressure), with the reactiontemperature of 45° C. and stirring. Then the catalyst was separated byprecipitation to give a solution of the pentanediamine. The resultingproduct was quantified by gas chromatography. 1,5-pentanediamine in thesolution after catalytic hydrogenation reaction was sampled andanalyzed. The results showed that 1,5-pentanediamine had a purity of99.51%, the content of 2,3,4,5-tetrahydropyridine was 0.007%, and thecontent of piperidine was 0.19% (normalized).

Comparative Example 1

To a 500 mL round bottom flask equipped with a stirrer and a thermometerwas charged 250 g of 1,5-pentanediamine in a mass concentration of 99%containing 500 mg of organic impurity THP (6 mmol, 0.2%).

Application Example

In a 100 L of enamel kettle, the air was replaced with nitrogen by meansof a vacuum purge gas and the enamel kettle was protected with nitrogen.A 40 kg aqueous solution of 1,5-pentanediamine was added to the kettleand the solution was heated to 60° C. with stirring. To the solution,adipic acid (made by PetroChina Liaoyang Petrochemical, the same below)was added to adjust pH of solution to 7.5, to prepare a solution ofpentanediamine adipic acid nylon salt.

In a 100 L polymerization kettle, the air was replaced with nitrogen andthe nylon salt solution was transferred to the polymerization kettle.The temperature of the oil bath rose to 230° C. When the pressure in thekettle rose to 1.73 MPa, a gas release will occur. When the temperaturein the kettle reached 265° C., the kettle was vacuumized to −0.06 MPa(vacuum gauge pressure), and this vacuum was maintained for 20 min, tomake the corresponding nylon.

The polymerization kettle was filled with nitrogen gas until thepressure thereof reached 0.5 MPa, and then the contents of the kettle ina melt state began to be discharged, and pelletized using a pelletizer.After drying under vacuum for 8 hours at 80° C., the color detection wascarried out.

The polyamide was prepared from the 1,5-pentanediamine obtained inExamples 1 to 10 and Comparative Example 1 according to above method,and the yellow index of the obtained polyamide was examined. The resultsare shown in Table 1.

TABLE 1 The Content of THP in the Purified 1,5-Pentanediamine YellowIndex of Nylon Example 1 0.06% 6 Example 2 0.05% 5 Example 3 0.04% 5Example 4 0.05% 6 Example 5 0.03% 4 Example 6 0.006%  2 Example 70.003%  1 Example 8 0.004%  1 Example 9 0.01% 3 Example 10 0.007%  2Comparative  0.2% 15 Example 1

Table 1 lists the content of THP in the 1,5-pentanediamine prepared inthe examples and comparative example of the present invention, and theyellow index of nylon prepared from above 1,5-pentanediamine as astarting material. The data in table 1 shows that the content of THP in1,5-pentanediamine can be controlled within 0.06% and the yellow indexof nylon is no more than 6 according to the purification method of thepresent invention. When the hydrogen gas is used as the catalyst for thereduction reaction, the content of THP can even be controlled within0.007%, such that the yellow index of the nylon is about 1. Comparedwith the comparative example, the yellow index is greatly reduced andthe quality is improved significantly.

Unless otherwise specified, the terms used in the present invention havethe meanings as commonly understood by one skilled in the art.

The embodiments described herein are for illustrative purposes only andare not intended to limit the scope of the invention. Variousalternatives, alterations and modifications can be made by one skilledin the art within the scope of the invention. The present invention isnot limited to the above-described embodiments, but only defined by theclaims.

1. A method for purifying 1,5-pentanediamine, comprising: providing1,5-pentanediamine to be purified; and treating said 1,5-pentanediamineto be purified by use of reduction reaction, to obtain purified1,5-pentanediamine.
 2. The method according to claim 1, wherein said1,5-pentanediamine to be purified contains 2,3,4,5-tetrahydropyridineimpurity.
 3. The method according to claim 1, wherein the content of2,3,4,5-tetrahydropyridine impurity in the purified 1,5-pentanediamineis less than 0.05 wt %.
 4. The method according to claim 1, wherein thecontent of 2,3,4,5-tetrahydropyridine impurity in the purified1,5-pentanediamine is less than 0.03 wt %.
 5. The method according toclaim 1, wherein the purified 1,5-pentanediamine contains piperidine. 6.The method according to claim 2, further comprising a distillation stepto remove the piperidine formed by the reduction of2,3,4,5-tetrahydropyridine, so that the content of piperidine in thepurified 1,5-pentanediamine is less than 0.05 wt %, based on the weightof 1,5-pentanediamine in the 1,5-pentanediamine to be purified.
 7. Themethod according to claim 6, wherein the content of piperidine in thepurified 1,5-pentanediamine is less than 0.03 wt %.
 8. The methodaccording claim 1, wherein said reduction reaction comprises anelectrochemical reduction or reduction by use of a reducing agent, saidreducing agent is hydrogen gas or metal hydride.
 9. The method accordingto claim 8, wherein the metal hydride is selected from one or more ofNaBH4, KBH4, LiA1H4.
 10. The method according to claim 8, wherein whenthe metal hydride is used as the reducing agent, the reactiontemperature is from 0 to 25° C. and the reaction time is from 0.5 to 1hour, and the metal hydride is from 1 to 2 times of2,3,4,5-tetrahydropyridine in the 1,5-pentanediamine to be purified inthe amount of substance.
 11. The method according to claim 8, whereinthe hydrogen gas is used as the reducing agent, and a nickel-basedcatalyst or a platinum-based catalyst is used simultaneously.
 12. Themethod according to claim 11, wherein said reduction reaction is carriedout by a fixed bed hydrogenation or a fluidized bed hydrogenation. 13.The method according to claim 12, wherein a fixed bed catalytichydrogenation is used, and the hydrogen pressure is from 0.5 to 12 MPaand the reaction temperature is from 40 to 110° C.
 14. The methodaccording to claim 12, wherein a fluidized bed catalytic hydrogenationis used, and the hydrogen pressure is from 0.5 to 15 MPa and thereaction temperature is from 40 to 110° C.
 15. A 1,5-pentanediamineprepared by the method according claim 1.